The problem with such rallies — Wall Streeters are cautious about using the term "bubble" until, of course, the bubble pops — is that they're lots of fun when on the way up and terrifying when they head in the other direction.
"The higher a market goes without a meaningful pullback, the deeper the fall when it finally does happen. Something will come along to pierce this market's enthusiasm," Krosby said. "If you're going to live by the stock market moving higher, you also have to be prepared to suffer the wrath when the market does pull back."
Despite the hazards that betting on a constantly rising market inherently entail, Trump has continued to pump up the market as a key measure of economic performance during his administration.
The president last tweeted about stocks on Jan. 13, boasting of a "big day" as the market hit yet another new high.
Making the gains all the more stunning is that they come amid ever escalating tensions on Capitol Hill that could yet lead to a government shutdown. That's aside from worries about nuclear war with North Korea, a hot-again battle over immigration, and as Trump faces a moribund approval rating that has been inversely correlated to economic growth and the stock rally.
"We've never seen a market that has been so divorced from the chaos and ongoing circus in Washington, so laser-focused on what's fundamentally better," said Art Hogan, chief market strategist at B. Riley FBR. "A strong fundamental backdrop seems to have taken the front burner and everything that in another place and time would have adversely affected us gets pushed to the back burner."
So if it's true that fundamentals are behind the market's willingness to discard headline risk, the argument that Trump is adding hot air to a bubble loses some steam. Unless ...
"At some point in time that won't be the case," Hogan said. "When that does happen, it's something that's not fundamental and can't be modeled, like leaving NAFTA or tweeting our way into a trade war."
Short of that, the market's willing to ride out the political warfare in Washington and watch Trump's tweets with an amusement foreign to much of the outside world, where pitched battles over the president's indelicate speech flood the airwaves on a daily basis.
In fact, investors have shown considerable willingness to tolerate and even thrive under political chaos over the years. The Philadelphia Fed even tracks partisan conflict on an index. The chart below shows an overlay of the index — spikes represent heightened tension — with the performance of the S&P 500.